1. Field of the Invention
This invention relates to an apparatus and method for producing a shell-like mold by introducing self-curing or gas-cured molding sand by vacuum sucking it into a shell-like cavity defined by a cope and a drag, wherein the amount of molding sand used is reduced.
2. Prior Art
Japanese Patent (A) 57-85643 discloses a method to produce a shell-like or thin mold to reduce the amount of molding sand to be used. As shown in FIG. 4 of the attached drawings, the method uses a drag 2 and a pattern 4 disposed above the drag to serve as a cope. The pattern 4, i.e., a cope, is spaced apart from the drag 2 so that the cope and drag define a shell-like cavity 6 therebetween. The drag has a plurality of vertical sucking throughbores 8 therein. The throughbores 8 are in communication with a vacuum source (not shown) through a duct 10. The pattern 4 at its perimeter has a plurality of molding-sand-supplying bores 12 through which molding sand is fed into the cavity 6. To introduce the molding sand into the cavity 6 and to produce a shell-like mold, the vacuum source is activated, and a vibratory table 14 on which the drag 2 is mounted is driven.
The method described above has the following drawbacks:
(a) As the pattern is disposed on the drag with the pattern surface facing downward, the molding sand charged in the cavity tends to move down due to gravity and due to the vibrations of the table, i.e., the sand tends to separate from the pattern surface. Thus the molding sand does not completely fill the cavity to the pattern surface. Accordingly, the desired shape of the mold, which must correspond to that of the pattern surface, cannot be obtained. PA1 (b) Since the pattern extends downward, it requires a plurality of molding-sand-supplying bores at its perimeter. When such bores are used, generally the amount of molding sand fed or sucked through each bore 12 differs, and therefore an extra amount of molding sand must be previously prepared in a hopper. This contradicts the purpose of the invention, which is to minimize the amount of sand used. PA1 (c) Since the sand in the bores 12 remains on the surface of the produced mold, troublesome work to remove the remaining sand is necessary. PA1 (d) As a plurality of throughbores 8, which communicate with the cavity, are disposed, the sand tends to accumulate at the entrances of the throughbores 8 (in FIG. 4 only one throughbore where the sand accumulates is shown, and it is designated by 16). This accumulated sand prevents the molding sand from flowing to a neighboring throughbore.